Control of electrolytic processes



Sept. 23, 1947. J. R. ERBE CONTROL OF ELECTROLYTIC PROCESSES Filed Dec.8, 1942 m M 9 Z a 0 F m a INVENTOR (fa/7n K, Erfie, L 61 ATTO EYWITNESSES: M/ I %z?@ Wm Patented Sept. 23, 1947 2,427,771 CONTROL OFELECTROLYTIC PROCESSES John R. Erbc, Pittsburgh 16, Pa.., assignor toWestinghouse Electric Corporation, East Pittsburgh, Pa., a corporationof Pennsylvania Application December 8, 1942, Serial No. 468,217

The present invention relates, generally, to the control of electrolyticprocesses, and, more particularly, to the control of the electrolytictreatment of continuously moving lengths of material.

In the manufacture of metal coated or plated materials such astin-plate, it has been the practice to apply the coating material to thematerial to be coated by dipping it into the molten coating material. Ithas been found that this process is wasteful of the coating material forthe reason that it is very difiicult to control the thickness of thecoating and, as a consequence, much more of the coating material is usedthan is necessary to properly coat the material for the purpose forwhich it is to be used.

It has been found that such'metal coatings may be applied very uniformlyby electrolytic means, and long sheets of material have been thus coatedby passing them through an electrolytic bath. The amount of materialdeposited electrolytically is a function of the length of time thematerial to be coated is exposed to the plating current and the densityof the plating current. It will be apparent, then, that a uniformdeposit of coating material will be made upon a strip of material as itmoves at a constant speed through an electrolytic bath and the currentdensity is kept constant.

In order to expedite the production of plated material by thiselectrolytic process, it has been proposed that the process be madecontinuous by securing the ends of successive lengths of'materialtogether as they are fed to the plating apparatus to thereby avoidstopping the length of material and the plating apparatus for thepurpose of threading each new length of material through the platingapparatus. In the operation of such a continuous plating system it isnecessary that the speed of travel of the length of material through theplating apparatus be decreased materially When the next succeedinglength of material is to be attached thereto to form the continuouslength of material. It will be apparent that this decrease of the speedof the length of material through the plating bath will cause the lengthof material to be acted upon by the plating current for a greater periodof time than when it is traveling at normal speed and it will benecessary to decrease the density of the plating current to prevent thedeposition of an excess quantity of coating material.

An object of the present invention is to provide a control system for acontinuous electrolytic process which shall function to coordinate thespeed and current density in the process.

Another object of the invention is to provide a. control system for anelectrolytic process for continuously treating a continuously movinglength of material which shall function to so 7 Claims. (Cl. 204-211)coordinate the current density and the speed of travel of the length ofmaterial as to produce uniform treatment of the length of materialregardless of changes in the speed of travel of the length of material.

A further object of the invention is to provide a control system for anelectrolytic plating process for plating a continuously moving length ofmaterial which shall function to so coordinate the speed of travel ofthe length of material and the plating current density as to produce auniform plate thickness regardless of changes in the speed of travel ofthe length of material through the electrolyte.

These and other objects and advantages of the invention will beapparentv from the following detailed description taken in connectionwith the accompanying drawing the single figure of which is adiagrammatic representation of an electrolytic plating system embodyingthe principal features of a preferred embodiment of the invention.

Referring to the drawing, a strip of material 2 is drawn through anelectrolyte 4 in a tank 6 by means of a motor 8 which drives rollmembers I0 and I2 Which in turn engage the strip 2. The armature of themotor 8 is connected to be energized by a generator [4 whose outputpotential may be varied by a rheostat l6 which varies the energizationof its field winding Hi. The generator [4 may be driven by any suitablemeans such as a substantially constant speed alternating current motor20.

A plurality of plating generators, such as generators 22 and 24, may bedriven by the motor 20 and connected by means of conductors 26 and 28 toseparate sets of plating electrodes 30 and 32. The other terminals ofthe generators 22 and 24 are connected by means of a common conductor 34to contact rolls 36 and 38 which engage the strip 2 as it passes throughthe electrolyte. Pilot generators 40 and 42 are connected to be drivenby the motor 8 and their speeds are, therefore, proportional to thespeed of travel of the strip 2 through the electrolyte 4. Generators 44and 46 may be continuously driven by any suitable means such as asubstantially constant speed alternating current motor 48. Thegenerators 40 and 46 are connected in series circuit relation as shownto energize the field windings 50 and 52 of the plating generators 22and 24, respectively, through variable resistors 54 and 56,respectively.

The generator 44 has a field Winding 58 which is energized through avariable resistor 60 by the potential drop across a shunt device 62 inthe common conductor 34 of the platirig current circuit. The excitationof the generator 44 thus varies in ccordance with the plating currentand its output potential is, therefore, a measure of the plating currentdensity. A regulator 54 functions to control a variable resistor 65which is connected in series circuit with a variable resistor 65 and thefield winding 68 of the generator 46 so that the output potential of thegenerator 46 is varied in accordance with the setting of the variableresistor 65 by the regulator 64.

The regulator 64 comprises a reversible motor l5 which is connected indriving relation with the variable resistor 65 and which may be made torotate in a reverse or forward direction by means of a movable contactelement 12 in co operation with fixed contact elements 14 and 16. Themovable contact element 12 is mounted upon a pivoted arm 13 which isdisposed to be operated in opposite directions by solenoids l8 and 80.

The solenoid 18 is connected as shown to be energized by the pilotgenerator 42 and thus acts upon the pivoted arm 13 with a forceproportional to the speed of the strip 2 through the electrolyte 4. Thesolenoid 80 is connected to be energized by the output potential of thegenerator 44 and, therefore, acts upon the pivoted arm 13 with a forcewhich is proportional to the density of the plating current.

In the operation of the system, since the output potential of the pilotgenerator 40 is proportional to the speed of the strip 2 through theelectrolyte 4, the excitation of the plating generators 22 and 24 willvary in accordance with the speed of the strip 2, and, since the platingcurrent varies in accordance with the output potential of the platinggenerators 22 and 24, the plating current will also vary in accordancewith the speed of the strip 2. The variable resistor 60 may function asa calibrating resistor to fix the desired ratio or proportionalitybetween the speed of the strip 2 and the plating current. If there isany variation in the proportionality between the speed of the strip 2and the plating current, the resulting unbalance of the forces acting onthe pivoted arm 13 will cause the contact element F2 to engage one ofthe fixed contact elements M and '16 which in turn will cause the motorto operate the variation resistor 65 in such a direction as to cause thegenerator 45 to add to or subtract from the excitation of the generators22 and 24 to thereby compensate for the variation in the proportionalitybetween the speed of the strip 2 and the plating current.

In order to obtain the best plating results it may be desirable that theplating current provided by one of the generators 22 and 24 be greaterthan the other. The variable resistors 54 and 56 are provided to soproportion the excitations of the plating generators 22 and 24 as toproduce any desired proportionality between the plating currentsprovided by these generators.

When it is desired to reduce the speed of the strip 2 to such a speed asWill permit the attachment of the leading end of a succeeding strip ofmaterial to the following end of the strip to thereby provide acontinuous process and continuous movement of the strip 2, the speed ofthe strip 2 may be reduced by reducing the excitation of the generator Mby means of the variable resistor 16. When the speed of the strip 2 isthus reduced, the output potential of the generator 46 will be reducedproportionally which in turn will cause a proportionate reduction of theexcitation of and, therefore, the plating current provided by theplating generators 22 and 24. The regulator 64 will function in responseto the speed of the strip 2 and the plating current density tocompensate for any variations in the proportionality of the speed of thestrip 2 nd plating current. Thus the desired amount of coating materialwhich is to be deposited on the strip 2 will be substantially the sameregardless of variations in the speed of the strip 2.

It is to be understood that the regulator 64 is merely illustrative ofone type of regulator that may be employed to perform the regulatorfunction described herein, and that any regulator that will function inresponse to potentials proportional to the speed of the strip and theplating current may be employed.

It is also to be understood that only two plating generators have beenshown and described herein merely for the purpose of illustration andthat as many plating generators as desired may be employed andcontrolled in accordance with the principles described herein.

It is also to be understood that the description of the electrolyticprocess as an electroplating process is merely illustrative of theprinciples of operation of the control system and that the controlsystem may be employed if desired in any electrolytic process in whichit is desired that a current density in the electrolytic process vary inany desired manner in response to variations in the speed of the lengthof material which is being electrolytically treated in the process.

Thus it will be seen that I have provided a control system for anelectrolytic plating process for plating a continuously moving length ofmaterial which shall function to so coordinate the speed of travel ofthe length of the material and the current plating density as to produceuniform plate thickness regardless of the speed of travel of the lengthof the material through the electrolyte.

In compliance with the requirements of the patent statutes, I have shownand described herein a preferred embodiment of my invention. It is to beunderstood, however, that the invention is not limited to the preciseconstruction shown and described but is capable of modification by oneskilled in the art, the embodiment herein shown being merelyillustrative of the principles of my invention.

I claim as my invention:

1. In a control system for an electrolytic process, generator means forsupplying current to the electrolytic process, an exciter for saidgenerator means, means for varying the excitation of said generatormeans in accordance with the speed of travel of a length of materialthrough the electrolytic process, and means for varying the ex citationof the exciter means in accordance with the variation of theproportionality between the speed of the length of material and thecurrent supplied to the electrolytic process.

2. In a control system for an electrolytic process, generator means forsupplying current to the electrolytic process, exciter means for varyingthe excitation of the generator means, means responsive to the speed oftravel of a length of material through the electrolytic process forvarying the excitation of said generator means, and regulator meansresponsive to the variation of the proportionality between the speed ofthe length of material and the current supplied to the electrolyticprocess for controlling said exciter means for further varying theexcitation of said generator means independently of said speedresponsive means.

3. In a control system for an electrolytic process employing anelectrolytic bath through which a length of material is moved, maingenerator means for supplying current to the electrolytic process, apilot generator, means for driving the pilot generator at a speedproportional to the speed of travel of a length of material through thebath, an auxiliary generator, means connecting said pilot generator andsaid auxiliary generator in series circuit relation to excite said maingenerator means, and means including regulator means jointly responsiveto the variations of the proportionality between the speed of the lengthof material and the current supplied t the electrolytic process forvarying the excitation of the auxiliary generator, whereby said pilotgenerator and auxiliary generator cooperate to so control the excitationof the main generator means as to maintain a predetermined ratio betweenthe speed of the material and the current supplied to the bathregardless of the speed of the material.

4. In a control system for an electrolytic process wherein a length ofmaterial is moved through the process, main generator means forsupplying current to the process, a first pilot generator operable todevelop an output potential proportional to the speed of the movingmaterial, an auxiliary generator, circuit means connecting said firstpilot enerator and said auxiliary generator in series circuit relationto the excitation circuit of the main generator means, said first pilotexciter functioning to vary the excitation of the main generator meansin accordance with the speed of the moving material, a second pilotgenerator operable to develop an output potential proportional to thespeed of said material, a third pilot generator operable to develop anoutput potential proportional to the current supplied to the process bythe main generator means, and regulator means jointly responsive to theoutput potentials of said second and third pilot generators forcontrolling the output potential of the auxiliary generator thereby tomaintain a predetermined ratio between the speed of the moving materialand the current supplied to the process.

5. In a control system for an electrolytic process wherein a length ofmaterial is moved through the process, main generator means forsupplying current to the process, a first pilot generator operable todevelop an output potential proportional to the speed of the movingmaterial, an auxiliary generator, circuit means connecting said firstpilot generator and said auxiliary generator in series circuit relationto the excitation circuit of the main generator means, said first pilotexciter functioning to vary the excitation of the main generator meansin accordance with the speed of the moving material, a second pilotgenerator operable to develop an output potential proportional to thespeed of said material, a third pilot generator operable to develop anoutput potential proportional to the current supplied to the process bythe main generator means, a motor-operated rheostat for controlling theexcitation of the auxiliary generator, and a differential relay jointlyresponsive to the output potentials of said second and third pilotgenerators for controlling the operation of the motor-operated rheostat,thereby to maintain a predetermined ratio between the speed of themoving material and the current supplied to the process.

6. In a control system for an electrolytic process wherein a length ofmaterial is moved through an electrolytic bath, a main generator forsupwhereby the pilot generator and regulator means function together toso control the output current of the main generator as to maintain apredetermined ratio between the speed of travel of the material throughthe bath and the current supplied to the bath regardless of the speed,and means operable to control the regulator means to vary said regulatormeans to vary said ratio of speed and current.

7. In a control system for an electrolytic process wherein a length ofmaterial is moved through an electrolytic bath, a main generator forsupplying variable amounts of current to the bath, said generator havinga field excitation winding, a variable voltage exciter for the maingenerator, a first pilot generator operable to develop an output voltageproportional to the speed of movement of the material through the bath,circuit means connecting the exciter and said pilot generator in seriescircuit relation with the field excitation winding of the maingenerator, whereby the current supplied to the bath is roughlyproportional to the speed of the material, a second pilot generatoroperable to develop an output voltage proportional to the speed ofmovement of the material, a third pilot generator operable to develop anoutput voltage proportional to the current supplied to the bath by themain generator, regulator means jointly responsive to the outputvoltages of the second and third pilot generators operable to controlthe excitation of the variable voltage exciter thereby to cause theariable voltage exciter to cooperate with said first pilot generator inthe control of the output current of the main generator to maintain apredetermined proportionality between the speed of the moving materialand the current supplied to the bath regardless of the speed at whichthe material is moved through the bath, and means operable to vary thevoltage output of the said third pilot generator independently of thecurrent output of the main generator to cause the regulator to maintainany desired ratio of speed and'current.

JOHN R. ERBE.

REFERENCES CITED The following references are of record in the

